Abstract Suicide is one of the leading causes of death in adolescence. To improve our ability to predict and prevent suicidal behavior, there is a pressing need for research in this area to advance beyond identifying risk factors toward a greater focus on the mechanisms of risk for this behavior. In particular, elucidating the neural pathways underlying risk for suicidal behavior is important insofar as such work may yield specific and modifiable targets for clinical intervention. The adoption of new experimental paradigms providing experimental control over potentially modifiable risk factors has been recommended as a means of meaningfully advancing the field in this regard. Although yet to be applied to the study of suicidality, transcranial direct current stimulation (tDCS), in conjunction with measures of electroencephalography (EEG) and event-related potentials (ERPs), may hold promise as an experimental paradigm in the study of potentially modifiable risk factors, and underlying neural mechanisms, for suicidality. One such risk factor of particular relevance to suicide in adolescence is state-sensitive aspects of impulsivity. Impulsivity has been consistently linked with suicidality, with this association appearing to be stronger in adolescence than adulthood. As a first step toward investigating whether modulation of impulsivity and associated neural pathways may yield clinically meaningful changes in risk for adolescent suicidal behavior, the proposed R21 is a proof-of-concept study evaluating the potential for tDCS targeting brain regions associated with behavioral impulsivity (right inferior frontal gyrus [rIFG]) and cognitive impulsivity (left orbitofrontal cortex [lOFC]) to modulate these facets of impulsivity in a sample of adolescent suicide attempters. Participants will be randomly assigned to receive anodal tDCS over the rIFG, anodal tDCS over the lOFC, or a sham stimulation condition, in a three-group design. Task-based measures of behavioral and cognitive impulsivity will be administered before and after tDCS or sham stimulation. Additionally, EEG and ERP data will be collected during the impulsivity tasks, and resting-state EEG data will be collected pre- and post-tDCS administration to confirm engagement of the targeted brain regions and to delineating the neural pathways underlying the effects of tDCS on impulsivity. This study is relevant to the research objective, of clarifying the neural circuitry profiles related to suicide risk, outlined by the NIH and the National Action Alliance for Suicide Prevention in their recent research agenda for suicide prevention. It is also consistent with NIMH?s Strategic Plan, which emphasizes the need for research on biomarkers and behavioral indicators of psychopathology, and for research utilizing neurobehavioral methodologies.